This invention relates to a bridge superstructure, and more particularly relates to the construction of a concrete deck made of precast concrete slabs and which rest on a series of precast concrete beams or steel girders.
Typically, the construction of bridges is a time consuming task where precast concrete support beams or steel girders are erected on location and customized form work is created between the beams in order to support concrete to be poured onto the form work. To some extent, the form work which is made from wood beams and plywood may be pre-fabricated but all the components must be trimmed to their final dimensions and assembled on location. After the poured concrete deck has set, the form work is removed. In order to minimize the danger of materials falling from scaffolding onto an underlying roadway and to minimize disruptions to traffic flow, such form work is typically erected and dismantled at night when the roadway is less busy and the roadway may be closed to general circulation.
A system for building a concrete deck with precast concrete slabs is described in U.S. Pat. No. 4,604,841. The slabs are reinforced with prestressed reinforcement rods which must extend throughout the width of the deck across support beams and through adjacent slabs. Because the precast slabs and prestressed rod system is unwieldy, the invention described in U.S. Pat. No. 4,604,841 proposes a precast slab having a width which corresponds to the width of the bridge and which has prestressed reinforcement rods extending throughout the width of the precast slab. The sheer size of such a slab is in itself a deterrent to its use since it is very heavy and difficult to manipulate.
Another problem which is encountered with decks constructed with precast slabs occurs at the joint between slabs placed end to end along the length of the bridge. Because of imperfections inherent in pouring concrete, and the likelihood of slabs becoming damaged during transportation, particularly at the bottom edges of slabs having large dimensions, the forward and trailing edges often do not mate. As a result, some form of sealant must be applied to the joints between slabs before pouring a concrete topping to build the deck to the required thickness.
An object of this invention is to simplify the construction of a bridge superstructure in order to minimize the time required for creating a concrete deck and to minimize the safety hazards to both the patrons using the roadway and the personnel who erect such structures, usually at night, when visibility is poor.
In accordance with this invention, there is provided a precast concrete slab which is dimensioned to locate between beams and which is reinforced with steel rods at predetermined spaced locations, a selected number of said reinforcement bars extending upwardly above the surface of the precast concrete slab to define anchors for securing a concrete topping to be poured onto the precast concrete slab.
The reinforcement bars comprising said anchors are preferably bent into a castellated shape of which inverted U-shaped portions extend above the surface of the precast concrete slab.
Preferably, the slabs are shaped to abut on each other end to end and have chamfered bottom edges to ensure mating of the upper edges on slabs disposed adjacent to one another.
In accordance with another aspect of the invention, a bridge is constructed by first erecting support beams at predetermined spaced locations and by placing screed adjusters comprising high density expanded polystyrene foam strips along opposed lateral edges of the support beams, locating precast slabs made according to the invention on said screed adjusters to bridge the spaces defined between the beams and form a deck, and pouring a fresh concrete topping over said deck to build the deck to a final pre-determined thickness in accordance with prevailing design considerations. Preferably, the precast slabs are coupled to anchors in the support beams with deck reinforcement bars and ties securing the deck reinforcement bars to the beam anchors and to the slab reinforcement bars.